1. Field of the Invention
The present invention relates to the distribution of house reference signals. More specifically, the present invention relates to the use of isochronous network packets to deliver house reference signals.
2. Background Information
As advancements in audio/video technology continue to be made, conventional analog audio/video technology is increasingly being replaced by newer digital audio and video systems and data transport mechanisms. Moreover, distribution of audio and video data over digital networks is rapidly becoming commonplace. Unfortunately, however, unlike their plain text counterpart, audio and video (i.e. multimedia) data tends to be resource intensive requiring large amounts of bandwidth when transmitted across networks. Furthermore, due to its dynamic nature, multimedia data does not easily lend itself for use within common asynchronous data transmission networks, whereby data transmission is guaranteed but the amount of time it takes to transfer the data is not. In contrast, isochronous networks, utilize time-stamping techniques and the concept of data transfer cycles to enable near real time transmission of time-dependent data. Although isochronous networks do not guarantee that a given packet will be delivered, on average the multimedia data delivery time will appear more constant as compared to an asynchronous network.
In conventional isochronous data networks, large amounts of digital data are xe2x80x9cpacketizedxe2x80x9d into many smaller data segments. Each data segment is stamped with appropriate timing information, such as for example, that provided by a house reference signal, before the data segments or packets are transmitted. Once the data packet is modified to include the timing information, the time-stamped data packet is attached to a packet delivery header which includes delivery information identifying the source and appropriate destination nodes on the network. Once received by a destination node, the data packets are reassembled and processed according to the designated function of the destination node.
Additional information regarding the operation and configuration of isochronous data networks may be found within the IEEE 1394 Standard. The IEEE Standard for a High Performance Serial Bus, IEEE Std. 1394-1995 published Aug. 30, 1996 (1394-1995 Standard) and its progeny provide a high speed serial protocol which permits implementation of high speed data transfers of both asynchronous and isochronous data. The existing progeny includes P1394a Draft Standard for a High Performance Serial Bus (1394a Standard) and P1394b Draft Standard for a High Performance Serial Bus (1394b Standard). Generically, networks implementing 1394-1995, 1394a, 1394b or subsequent revisions and modifications thereof are referred to herein as IEEE 1394 networks. Similarly, additional information regarding a general isochronous packet format may be found in the International Electrotechnical Commission standard 61883-1:1998-02 (hereinafter xe2x80x9cIEC 61883xe2x80x9d). 
Most professional audio and video applications are typically equipped to process and manipulate input signals from various audio and video sources. In an audio and/or video editing application, for example, multiple independent audio and video input signals may be received from a variety of sources and subsequently mixed together to form a single coherent audio/video production. In order to properly mix the audio/video input signals from such sources, however, the operation of the sources, as well as other non-source devices within the audio/video system, must be synchronized with respect to time. One way this may be achieved is by locking the operation of the audio/video devices to a common house reference signal. By each device independently referencing a common distributed timing signal, all of the devices should operate in synchronization. House reference signals are typically clock signals that are distributed to the various audio and video devices throughout a studio or plant via one or more dedicated coaxial cables. One problem with such a house reference distribution model, however, is the reliance on outmoded cabling which merely serves the single purpose of distributing the house reference signal.
A method of distributing video reference signals is described. In one embodiment a source reference signal including source data is received by a first device. An isochronous network packet is in turn generated by the first device based at least in part on the source reference signal and to the exclusion of the source data. Once generated, the isochronous network packet is transmitted by the first device to a secondary device to synchronize timing between the first and secondary devices.